Dark Spot Defects Research Articles

Tem study of dark line defect growth from dislocation clusters in (GaAl)As-GaAs double heterostructure lasers

Dark spot defects in (GaAl)As-GaAs double heterostructure lasers are studied by transmission electron microscopy and found to be a cluster of dislocations generated in the first (GaAl)As epitaxial layer during epitaxial growth. Burgers vectors and spatial configuration of dislocation dipoles developing from these dislocations are determined. It is found that Burgers vectors of dislocations in the dislocation cluster obey the Burgers vector sum rule.

Degradation of GaAs0.9P0.1 LED's Operating at High Current Densities

Degradation of GaAs0.9P0.1 LED's under high stress current densities (≧0.8 kA/cm2) are studied for optical fiber communication systems. The degradation modes are divided into two categories: initial rapid degradation and long term degradation. The former corresponds to the formation of dark spot defects (DSD's), <110> and <100> oriented dark line defects (DLD's). Among them frequent of <110 > DLD's due to internal stress present in the GaAs–GaAs0.9P0.1 epitaxial structure is typical of these LED's.The latter is characterized by formation of nonradiative recombination centers near the P-N junction. At this stage of degradation DSD's and DLD's show little change in their size and shape, and the gradient of the ionized impurity distribution near the P-N junction decreases, which implies that ionized impurities are transferred to the junction, where they are accumulated and precipitated, contributing to the formation of nonradiative centers.

Reduction of crystal defects in active layers of GaAs-AlGaAs double-heterostructure lasers for long-life operation

The influence of oxygen in ambient gas during liquid-phase epitaxial growth on a double-heterostructure (DH) wafer is investigated. The oxygen incorporated into grown layers seems to be associated with the formation of crystal defects such as so-called dark-spot defects (DSD's) and saucer pits. When the oxygen concentration is reduced less than 0.03 ppm, crystal defects such as DSD's and saucer pits drastically decrease in the epitaxial layers. Al added into Ga solutions behaves as the getter of the oxygen in the Ga solutions and prevents the formation of DSD's in the active layers. The correlation between DSD's and etch pits is examined. All of the dislocations do not always contribute to the formation of DSD's. The formation of DSD's depends on oxygen concentration in the ambient hydrogen gas. In DH lasers fabricated from DH wafers grown under the extremely low oxygen concentration, the operating life at room temperature exceeds 10 000 h at the present time.

Influence of Oxygen in Ambient Gas on LPE GaAs Layers

The influence of oxygen in ambient gas on liquid phase epitaxial GaAs layers is investigated. The oxygen concentration in the ambient gas during liquid phase epitaxial growth is quantitatively measured. The carrier concentration increases from 1×1015 cm-3 to 2.5×1017 cm-3 in proportion to the oxygen concentration in the ambient gas. The saucer pit density produced by molten KOH etchant and the relative emission intensity of photoluminescence spectra due to deep levels drastically decrease in the undoped GaAs layers grown under the oxygen concentration less than 0.03 ppm. The density of dark spot defects is also reduced to a few hundred per square centimeter in the Si-doped GaAs layers grown on Te-doped GaAlAs layers under the oxygen concentration less than 0.03 ppm. The oxygen incorporated into grown layers seems to be related with the formation of those defects.

V-6 a method for the prevention of the formation of dark-line and dark-spot defects in GaAlAs double heterostructure lasers

V-6 a method for the prevention of the formation of dark-line and dark-spot defects in GaAlAs double heterostructure lasers

Suppression of defect formation in GaAs layers by removing oxygen in LPE

The oxygen concentration in the ambient gas during liquid phase epitaxial growth processes was quantitatively analyzed. The oxygen influences the formation of defects such as saucer pits and so-called ’’dark spot defects’’ and the carrier concentration of grown layers. Reducing the oxygen concentration less than 0.03 ppm, the defect densities drastically decrease in GaAs grown layers.

X-Ray Topographic Study of Lattice Defects Related with Degradation of GaAs-Ga1-xAlxAs Double-Heterostructure Lasers

Dark-spot defects (DSD) which are primary sources of the rapid degradation of GaAs-Ga1-xAlxAs double-heterostructure (DH) lasers are studied by X-ray topography. X-ray topographs of the defective parts of a DH wafer were obtained through the use of micro-X-ray topography. This technique is effective for small specimens of 0.01∼1 mm2. In addition, it is suggested that elimination of a dislocation from a DH wafer is possible, not by introducing a misfit dislocation, but by using a dislocation-free GaAs substrate.

X-ray topographic study of dark-spot defects in GaAs-Ga1−xAlxAs double-heterostructure wafers

Dark-spot defects (DSD) in a GaAs-Ga1−xAlxAs double-heterostructure (DH) wafer are studied by x-ray topography. Such DSD’s are one of the primary sources of the dark-line defects (DLD) that cause rapid degradation of GaAs-Ga1−xAlxAs DH lasers. By using x-ray topography almost all DSD’s observed by photoluminescence topography are correlated with dislocations in a GaAs substrate. In addition, it is observed that some dislocations in the substrate are not sources of DSD’s when the dislocation axes are nearly parallel to the surface of the substrate.

Degradation sources in GaAs-AlGaAs double-heterostructure lasers

Several sources of the dark-line defect (DLD) that causes rapid degradation of GaAs-AlGaAs double-heterostructure (DH) lasers have been identified by means of photoluminescence (PL) topography and a laser-induced degradation technique. All the sources that have been identified correspond to crystal defects, among which dark-spot defects (DSD) that are native to as-grown wafers are found to be most important. The growth and propagation processes of DLD's and DSD's have also been investigated. These defects are found to be highly mobile under high-intensity laser pumping. The correlation between the substrate dislocations and the DSD's has been examined by etching and X-ray topography. Although most DSD's correspond to etch-pits in epilayers, they are not always correlated with substrate dislocations.

An electron microscope investigation of fatigue deformation in copper

The initial fatigue deformation in copper has been shown to be characterised by the presence of deformation bands of high dislocation density, frequently found in conjunction with linear arrays of a dark spot defect. Also noted at this stage was the presence of heavily jogged dislocations. The final fatigue structure consisted of patches of very high dislocation density, occasionally aligned in a specific direction, resolvable as either round or elongated dislocation loops.